Fluids produced from wells often include multiple phases. For example, a conventional gas well can be used to produce hydrocarbon gases from a subterranean reservoir to a surface location. The reservoir where the gas is found may also contain liquids, such as water or hydrocarbon liquids. In a typical completion of a gas well, a tubular casing having one or more radial layers is disposed from the surface location to or through the reservoir. A production tube or string, typically a steel pipe, is disposed within the casing, typically with an annulus defined between the outside of the production tube and the innermost well casing. At depth, the outer surface of the production tube is sealed to the inner surface of the casing by packers so that the production tube provides a pathway from the reservoir to the surface location, and all produced fluid flowing through the well from the reservoir to the surface location flows through the production tube. The casing is perforated to admit the produced fluid from the reservoir into the production tube.
Gas and liquid that are present in the reservoir may enter the casing. During a typical operation of a gas well, the level of water or other liquids in the casing is below the inlet of the production tube. Nevertheless, the flow of gas into the production tube may carry some liquid with it, a phenomenon referred to as “liquid loading” of the produced gas. Liquid loading can occur in different ways. For example, if liquid resides in the casing and the upper level of the liquid is near the inlet of the production tube, the flow of the gas into the production tube may disturb the upper level of the liquid and draw the liquid into the production tube. In fact, the upper level of the liquid in the immediate vicinity of the production tube may be temporarily pulled up to the inlet of the production tube. The liquid may temporarily block the gas from entering the production tube. In this way, a distinct “slug” of liquid may be drawn into the tube before the level of the liquid in the casing falls back down, and the slug then passes upward through the tube with the gas.
Alternatively, even if the upper level of the liquid remains below the inlet of the production tube, the gas may carry some liquid. In some cases, the liquid can be carried first in a gaseous phase, e.g., as water vapor, that liquefies as the produced fluid travels through the production tube. As the vapor liquefies, it can form a mist, i.e., small droplets suspended in the gas. Mist-like droplets of the liquid can also be present in the gas as it enters the production tube. In either case, the droplets of liquid typically tend to combine and form larger drops of liquid in the produced fluid. Thus, as the produced fluid travels through the production tube, the liquid content may increase and may become more difficult to lift, thereby reducing the flow rate of the well. The liquid content in the produced fluid may even stop the production of gas from the well until sufficient pressure builds.
There are several conventional methods for deliquification of a gas well such as by direct pumping (e.g., sucker rod pumps, electrical submersible pumps, progressive cavity pumps). Another common method is to run a reduced diameter (e.g., 0.25 to 1.5 inches) velocity or siphon string into the production well. The velocity or siphon string is used to reduce the production flow area, thereby increasing gas flow velocity through the string and attempting to carry some of the liquids to the surface as well. Another alternative method is the use of plunger lift systems, where small amounts of accumulated fluid is intermittently pushed to the surface by a plunger that is dropped down the production string and rises back to the top of the wellhead as the well shutoff valve is cyclically closed and opened, respectively. Another method is gas lift, in which gas is injected downhole to displace the well fluid in production tubing string such that the hydrostatic pressure is reduced and gas is able to resume flowing. Additional deliquification methods previously implemented include adding wellhead compression and injection of soap sticks or foamers.
Although there are several conventional methods for removing liquids from a well, there exists a continued need for improvements to produce fluids from a well, particularly in the production of gas from reservoirs that include liquid content.